Despite the promise of preclinical models for systemic gene therapy to liver, lung, and other tissues, there is currently no commercial gene therapy product on the market. The failure of most human gene therapy clinical trials to treat metabolic disorders and cancer has been ascribed to the relative inefficiency of viral and non-viral gene transfer systems. Viral vectors have been used for most gene therapy studies because of their ability to efficiently infect cells in tissue culture. However, an enormous payload of particles needs to be applied in an intravenous injection to transduce cells in vivo, and toxicities of viral vectors are well documented [1], including a recent lethal toxicity that occurred following a portal vein injection of recombinant adenovirus [2]. In contrast, non-viral systems are generally felt to be safe although inefficient. There is a growing consensus that non-viral systems will be the vector of choice for in vivo applications once gene transfer efficiency is improved.
Several barriers restrict non-viral methods of gene transfer, including: i) particle stability in blood and interstitial tissues; ii) ability of the gene transfer particle to exit capillaries and travel to parenchymal cells; iii) cell entry via receptor-mediated endocytosis or cell fusion; iv) stability in and escape from endosomal and lysosomal compartments; v) diffusion rate in the cytoplasm; vi) nuclear pore transit; and vii) “uncoating” of DNA to permit biological function in the nucleus. For example, numerous publications have documented the failure of non-viral methods to transfect post-mitotic, growth-arrested cells [3-11], presumably because the intact nuclear membrane of non-dividing cells restricts entry of naked DNA into the nucleus via the 25 nm nuclear pore [12-13].
Thus there is a continuing need in the art for improved formulations and methods for delivery of genes to animals and humans. In addition, there is a need in the art for formulations which will be stable to storage and retain biological activity.